remora

A ray-finned fish of any species in the family Echeneidae, which have dorsal fins adapted into a suction device. Using this device, they attach themselves to larger marine animals with which they form symbiotic relationships, removing parasites in return for protection and transport. In popular culture, remoras are best-known for attaching themselves to sharks (hence the common name "sharksucker"), though they have been known to attach themselves to turtles, whales, and even human divers.